body,h1,h2,h3,p,ul{
    margin: 0px;
    padding: 0px;
}
body{
    padding-top: 44px;
}
/*页面头部*/
.nav{
    /*定宽居中*/
    width: 1000px;
    margin: 0px auto;
    /*background-color: red;*/
}
#logo{
    height: 40px;
}
.nav>ul{
    list-style: none;
    float: right;
    line-height: 44px;
}
.nav ul li{
    float: left;
    margin-left: 20px;
}
.nav ul li a{
    color: black;
    text-decoration: none;
}
.nav ul li a:hover{
    text-decoration: underline;
}
.header{
    box-shadow: 1px 1px 3px gray;
    position: fixed;
    top: 0px;
    width: 100%;
    background-color: white;

    z-index: 1;
}

/*横幅*/
.banner img{
    width: 100%;
}

/*主要内容*/
.main{
    /*margin-top: 20px;*/
    width: 1000px;
    margin: 20px auto 0px;
}
.main p{
    text-indent: 2em;
    line-height: 24px;
}
.main div{
    margin-top: 20px;
}
.main h2::before{
    content: '\25AE';
}
.main h2{
    color: orange;
}
.main div img{
    margin: 20px 0px;
    width: 100%;
}
#classmates div{
    height: 500px;
    background-image: url(images/classmates.jpg);

    position: relative;
}
#classmates div img{
    border-radius: 50%;
    position: absolute;
}
#classmates div img:nth-child(1){
    width: 200px;
    height: 200px;
    
    top: 60px;
    left: 30px;
}
#classmates div img:nth-child(2){
    width: 300px;
    height: 300px;
    
    top: 100px;
    left: 230px;
}
#classmates div img:nth-child(3){
    width: 240px;
    height: 240px;
    
    top: 80px;
    right: 30px;
}

/*页脚*/
.footer p{
    text-align: center;
    color: gray;
    width: 1000px;
    margin: 10px auto;
    padding: 20px;
    border-top: 1px solid gray;
}